Apparatus for detecting and/or measuring the concentration of oxygen in aqueous liquids such as boiler feed water



APPARATUS FR DE'i'ECTlNG AND/0R MEAS- URENG THE CQNCENTRATIN @il XYGEN 1N AQUEGUS UQUBS SUCH AS BBLER FEED WATER Arthur Gordon Bowson and Ivor Bohn Buckland, Londen, England, assignors, hy mcsne assignments, tc Engelhard industries lne., Newark, NJ., a corporation ci Delaware @riginal applicatien A g. 15, B56, Ser. No. 604,233.. Divided and this appiicatinn Sept. 3, 1953, Ser. No. 758,849

12 Claims. (Cl. 21M- 195) This invention relates to a method and apparatus for detecting and/or measuring the concentration of oxygen in aqueous liquids, for example the concentration of dissolved oxygen in boiler feed water.

It is often required that the concentration of dissolved oxygen in an aqueous liquid should be as low as possible. It is especially important to control the oxygen content of the feed water in steam boilers in power stattions, steam ships, and the like, since any oxygen dissolved in the feed water causes corrosion of the boiler tubes. Up to the present, the known methods of detecting and measuring the concentration of such oxygen are relatively insensitive, and sluggish in operation.

According to one aspect of the present invention, there is provided a method oi detecting and/ or measuring the concentration of oxygen in an aqueous liquid, wherein the liquid, the oxygen content ot which is to be determined, is caused to ow and an inert carrier gas (as hereinafter defined) is brought into intimate contact with the liquid in such a way that at least part of any oxygen contained in the liquid is transferred to the gas, the liquid and gas being thereafter separated one from the other, and wherein the gas so separated is caused to contact means adapted to give a response indicative of the amount of oxygen in the gas, the gas after contacting said means then being circulated for contact with further liquid.

According to another aspect of the present invention, there is provided apparatus for detecting and/ or measuring the concentration of oxygen in an aqueous liquid, wherein means adapted to give a response indicative of the amount of oxygen present in the ambient gas contacting said means, is disposed in a housing having an inlet and a gas outlet spaced from said inlet, there being means adapted to circulate as between said inlet and said outlet an inert carrier gas (as hereinafter defined) in tuch a way that the gas intimately contacts the liquid while the liquid is moving and that at least part of any oxygen contained in the liquid is transferred to the gas, the circulating means and/or the housing being so arranged that the gas is separated from the liquid before it is caused to contact the indicating means under the inlluence of the circulating means.

By the expression an inert carrier gas as used in this specication, there is meant a gas which will not cause a response on the indicating means, which will react neither with the liquid nor with the oxygen on being brought into contact with the latter at ordinary temperatures, and which, if dissolved in the liquid will deleteriously affect neither the liquid if the latter is required for further use, nor any apparatus in which the liquid is subsequently contained or used. Examples of such a gas are hydrogen, argon and nitrogen, hydrogen being the preferred gas.

For a better understanding of the invention, and to show how the same may be carried into eect, reference will now be made to the accompanying drawing, which is an elevational View of an apparatus for measuring the concentration of dissolved oxygen in an aqueous liquid.

tet

ananas Patented Dec. 3, 1953 Pice Referring now to the drawing, the apparatus comprises a tubular vessel 1 in which a galvanic cell 2 (shown partly in section) is disposed in a Vertical position, there being an annular space 3 between the cell 2 and the inner wall of the vessel 1. The cell 2 consists of a tube 4 of porous synthetic plastic material such as polyvinyl chloride having a porosity in the region of percent. The tube d is closed at its lower end, and is filled with an oxidizable anode material 5 consisting essentially of finely divided cadmium, and with an electrolyte consisting of an aqueous 5 percent solution of potassium hydroxide. The cathode d of the cell is constituted by coiled silver wire wound around the outside of the tube as at 7. A platinum wire ii is separately wound around the outside of the tube 4, the use of the platinum wire S being for charging the cell. Separate leads 9, 1@ and 11 extend from the silver wire cathode, the platinum wire, and the cadmium anode respectively, the leads 9, 1t) and 11 being sealed through a stopper 12 which closes the top ofthe vessel 1.

A gas outlet pipe 13 leads from the top of the vessel 1 to a container 14 which is provided at its top with a stopper 1S, and from which leads an outlet pipe 16 closed by a tap 17. The lower end of the container 1d is joined to the upper end of a chamber 18, the interior of the chamber 18 being in communication with the interior of the container 14 through a bent pipe 13A.

A liquid inlet pipe 19 is sealed into the wall of the chamber 18 and is arranged to discharge liquid into the chamber 13 at a location below the junction of the chamber 18 and the container 1d. An outlet pipe 2@ leads from the bottom of the chamber 1S into the vessel 1 at a location near the bottom thereof and below the lower end of the cell 2.

The outlet pipe 2l? has, at 21, a restriction in diameter where it joins the chamber 18.

The lower end of the vessel 1 is connected to a device 22 for maintaining a constant head of liquid in the bottom of the vessel below the lower end of the cell 2, the constant head of liquid acting as a gas-tight seal and preventing air from entering the apparatus.

A make-up hydrogen device 23 is attached to the top of the vessel 1 by a pipe 24 which leads into a tube 25. The tube 25 contains a dilute aqueous` electrolyte 26 such as dilute potassium hydroxide solution or dilute sulphuric acid and `the pipe 24 is arranged with its outlet below the level of the electrolyte 26 in the tube 25. A lead to an electrode 27 is sealed through the pipe 24 and the electrode 2.7 is located slightly above the liquid in the tube, while a further electrode 28 is immersed in the electrolyte. The tube 25 is closed by a stopper 29, but is open to the atmosphere through a sleeve 39 `which is located in the stopper 2.9' and through which the `lead to 4the electrolyte 28 passes. The electrodes 27 and 28 are connected to a battery (not shown) in such a way that the electrode 27 is la cathode.

An excess gas blow-olf device 31 is attached to the vessel 1 intermediate its ends, and consists of a pipe 3,2 leading from the vessel 1 into a tube 33 which is open to the atmosphere at 34. The tube 33 contains water and the pipe 32 is arranged with its end just `below the level of the water in the t-ube 33.

In the use of the apparatus just described, the apparatus is filled with hydrogen, and the container 14 is filled with a bed of palladium on alumina catalyst 34 on which hydrogen and oxygen can combine in arneless combustion at room temperature to produce water vapor. The liquid, e.g. water, the oxygen content of which is to be determined, en-ters the chamber 18 through the liquid inlet pipe 19. The water runs down the outlet pipe Ztl and, aided by the restriction 21 formed therein sucks some of the hydrogen into such pipe, iso producing a partial vacuum in the chamber after the manner of the well known laboratory lter pump, and thus causing a circulation of hydrogen up the annular space 3i, plast 'the galvanic cell 2, through the outlet pipe i3 and the container i4, and into the chamber 18 lwhere it is sucked down the outlet pipe 20 by the water.

The hydrogen is sucked down the outlet pipe 20 as bubbles so that the oxygen-containing water intimately contacts the hydrogen in such a way that a proportion of the oxygen dissolved in the water is released into the hydrogen. On discharging into the bottom of the vessel l, the water runs away through the constant head device 22, while the oxygenated hydrogen separates from the water :and flows upwardly past the galvanic cell Z, the silver cathode 6 of lwhich adsor-bs a proportion of the oxygen. An electric current is generated by the cell and is directly proportional to the lamount of oxygen in the ambient gas iowing past the cell.

Since the cell 2 may remove only a proportion of the oxygen dispersed in the gas, it will be appreciated that by plain re-circulation of the gas the proportion of oxygen in the circulating gas will increase progressively until equilibrium is substantially established. rlhis will not only cause the cell to generate a larger current, thus discharging the cell more rapidly, but following a change in oxygen content oi the incoming liquid, some time will 'elapse before a new equilibrium is established. The bed of catalyst 34 lin lthe container le insures that the oxygen which has not been adsorbed `on the cathode 6 of the cell 2 is converted into water vapor by reaction with the hydrogen, so that the incoming liquid is at all times, brought into Contact with oxygen-free hydrogen.

When hydrogen is used as the carrier gas, there will be a slight loss of hydrogen due to the reaction occurring in the `bed of catalyst. There will also be a slight loss of hydrogen which has dissolved in the liquid. It is therefore necessary to add hydrogen to the system to make up the 4loss and to maintain the system in the required balanced state. The hydrogen make-up device 23 serves to add the necessary hydrogen to the system.

When the pressure in the system decreases dueV to the combination and the dissolving of hydrogen, the liquid in pipe 24 rises, and makes contact with the electrode 27, thus causing a current to flow through the two electrodes V27 and Z8 and the electrolyte Z6. Since the electrode 27 is a cathode, hydrogen will be evolved at this electrode tand will ow into the system thus making good the hydrogen losses. When the pressure in the system reaches the required value, the liquid in the pipe 24 is forced back to its initial position, out of contact with the electrode 27, so that evolution of hydrogen ceases. However, should the pressure in the system rise beyond the required value, the excess gas blow-off device 31 will become operative and the excess gas will be `forced out to atmosphere through the pipe 32.

ln `the apparatus, the reaction at the galvanic cell is such as to cause the :anode material Ito be attacked and oxidized. The anode material is a gas metal which is readily attacked by .the electrolyte in the presence of oxygen, but which is not attacked in the absence of oxygen, :and the anode material may be iantimony, or massive lead, or preferably finely divided cadmium, in which case cadmium hydroxide Cd(OH)2 is formed at the anode.

The cathode may be `gold or platinum instead of silver, and the electrolyte of the cell, although preferably potas- .sium hydroxide solution, can be an acid electrolyte, it being essential that the electrolyte does not attack the lcathode either in the presence, or the absence of oxygen.

The galvanic cell employed in the apparatus may be modified, for example, by being made less sensitive in order to measure higher concentrations of oxygen, the .cell being one which will produce an electric current proportional to the concentration of oxygen in ygas supplied to the cell, and which will not produce a current in the absence of oxygen. However, the cell may be replaced by other known means for measuring the concentration of oxygen in 4the gas.

The `galvanic cell has .a signiicant temperature coefficient and for most accurate results it is preferable to insert the whole apparatus in a thermostatically controlled bath, although it may be sulicient to control the inlet temperature of the water.

In cases where the nature of the liquid or the process for which it is intended to be subsequently used preclude the use of hydrogen, another inert carrier gas (as hereinbefore defined) maybe employed, and in such cases the catalyst 34 with its container 14, and the hydrogen makeup device 23 -will not be included in the apparatus, and an alternative means of making up the inert carrier gas may be employed. The apparatus will still be useful, but the response of the apparatus to a chan-ge in the oxygen content of the liquid will be less rapid, although the magnitude of the response may be greater.

In other cases, it may not be necessary entirely to exclude hydrogen, land another inert carrier gas containing a small proportion of hydrogen, sufficient to react with the oxygen in the circulating gas, lmay be employed.

This application is a division of copending application Serial No. 604,233, iled August 15, 1956, now U.S. Patent No. 3,050,371,

What is claimed is:

l. In a device of the character described, means for mixing hydrogen with water containing dissolved oxygen, means for separating the gaseous and liquid phases, means for removing at least a portion of the oxygen from the separated gaseous phase by adsorption, and means for removing residual oxygen from the gaseous phase.

2. In a device of the character described, means for mixing hydrogen with water containing dissolved oxygen, means for separating the gaseous and liquid phases, means for removing at least a portion of the oxygen from the separated gaseous .phase by adsorption, and catalytic means for removing residual oxygen from the gaseous phase.

3. An oxygen analyzer comprising mixing means for mixing hydrogen with a liquid containing dissolved oxygen, the mixing means being connected to a conduit having a galvanic cell therein, catalytic means connected to the conduit, and means connecting the catalytic means with the mixing means.

4. An oxygen analyzer according to claim 3 in which the galvanic cell has a silver cathode.

5. An oxygen analyzer comprising mixing means for mixing hydrogen with water containing dissolved oxygen, the mixing means being connected to a conduit having separation means therein for separating the gaseous and liquid phases, a galvanic cell mounted in the conduit and adapted to be contacted by the separated gaseous phase, catalytic means connected to the conduit, and means connecting the catalytic means with the mixing means.

6. An oxygen analyzer comprising mixing means for mixing hydrogen with water containing dissolved oxygen, the mixing means being connected adjacent the lower end thereof to a substantially vertical conduit having separation means therein for separating the gaseous and liquid phases, a galvanic cell mounted in the conduit and adapted to be contacted by the separated gaseous phase, catalytic means connected to the conduit adjacent the upper end thereof, and means connecting the catalytic means with the mixing means.

7. An oxygen analyzer according to claim 6 in which the galvanic cell has a silver cathode.

8. An oxygen analyzer according to claim 6 in which means is connected to the conduit for applying additional hydrogen thereto.

9. An oxygen analyzer according to claim 6 in which the separation means is a pool of Water in the bottom of the conduit.

10. An oxygen analyzer according to claim 6 in which the catalytic means includes a supported palladium metal catalyst.

11. An oxygen analyzer according to claim 6 in which the galvanic cell has an anode comprising finely divided cadmium.

12. An oxygen analyzer according to claim 6 in which the electrolyte of the galvanic cell is a solution of potassiurn hydroxide.

References Cited in the file of this patent UNITED STATES PATENTS 

1. IN A DEVICE OF THE CHARACTER DESCRIBED, MEANS FOR MIXING HYDROGEN WITH WATER CONTAINING DISSOLVED OXYGEN, MEANS FOR SEPARATING THE GASEOUS AND LIQUID PHASES, MEANS FOR REMOVING AT LEAST A PORTION OF THE OXYGEN FROM THE SEPARATED GASEOUS PHASE BY ADSORPTION, AND MEANS FOR REMOVING RESIDUAL OXYGEN FROM THE GASEOUS PHASE. 